The Buddha taught that to realize enlightenment, a person must develop two qualities: wisdom and compassion. Wisdom and compassion are sometimes compared to two wings that work together to enable flying, or two eyes that work together to see deeply.
In the West, we're taught to think of "wisdom" as something that is primarily intellectual and "compassion" as something that is primarily emotional, and that these two things are separate and even incompatible. We're led to believe that fuzzy, sappy emotion gets in the way of clear, logical wisdom. But this is not a Buddhist understanding.
The Sanskrit word usually translated as "wisdom" is prajna (in Pali, panna). I understand this word could also be translated as "consciousness," "discernment," or "insight." The many schools of Buddhism understand prajna somewhat differently, but generally we could say that prajna is understanding or discernment of the Buddha's teaching, especially the teaching of anatta, no self.
The word usually translated as "compassion" is karuna, which is understood to mean active sympathy or a willingness to bear the pain of others. In practice, prajna gives rise to karuna, and karuna gives rise to prajna. Truly, you can't have one without the other. They are a means to realizing enlightenment, and they are also enlighenment manifested.
Compassion as Training
In Buddhism, the ideal of practice is to selflessly act to alleviate suffering wherever it appears. You may argue it is impossible to elminate suffering, and maybe it is, yet we're to respond anyway.
What does being nice to others have to do with enlightenment? For one thing, it helps us realize that "individual me" and "individual you" are mistaken ideas. And as long as we're stuck in the idea of "what's in it for me?" we are not yet wise.
In Being Upright: Zen and the Bodhisattva Precepts, Soto Zen teacher Reb Anderson wrote, "Reaching the limits of practice as a separate personal activity, we are ready to receive help from the compassionate realms beyond our discriminating awareness."
Reb Anderson continued, "We realize the intimate connection between the conventional truth and the ultimate truth through the practice of compassion. It is through compassion that we become thorougly grounded in the conventional truth and thus prepared to receive the ultimate truth. Compassion brings great warmth and kindness to both perspectives. It helps us to be flexible in our interpretation of the truth, and teaches us to give and receive help in practicing the precepts."
In The Essence of the Heart Sutra, His Holiness the Dalai Lama wrote,
"According to Buddhism, compassion is an aspiration, a state of mind, wanting others to be free from suffering. It's not passive -- it's not empathy alone -- but rather an empathetic altruism that actively strives to free others from suffering. Genuine compassion must have both wisdom and lovingkindness. That is to say, one must understand the nature of the suffering from which we wish to free others (this is wisdom), and one must experience deep intimacy and empathy with other sentient beings (this is lovingkindness)."
Have you ever seen someone do something courteous and then get angry for not being properly thanked? True compassion has no expectation of reward, even a simple "thank you," attached to it. Expecting a reward maintains the idea of a separate self and a separate other.
The ideal of dana paramita -- the perfection of giving -- is "no giver, no receiver." For this reason, traditionally begging monks receive alms silently and do not express thanks. Of course, in the conventional world there are givers and receivers, but it's important to remember that the act of giving is not possible without receiving. Thus, givers and receivers create each other, and one is not superior to the other.
That said, feeling and expressing gratitude chips away at our selfishness, so unless you are a begging monk it's all right to say "thank you" when appropriate.
To draw on an old joke, you get to be more compassionate the same way you get to Carnegie Hall -- practice.
It's already been noted that compassion arises from wisdom, just as wisdom arises from compassion. If you're feeling neither especially wise nor compassionate you may feel the whole project is hopeless. But the nun and teacher Pema Chodron says, "start where you are." Whatever mess your life is right now is the soil from which enlightenment may grow.
In truth, although you may take one step at a time, Buddhism is not a "one step at a time" process. Each of the eight parts of the Eightfold Path support all the other parts. Every step integrates all the steps.
That said, most people begin by better understanding their own suffering, which takes us back to prajna, wisdom. Usually meditation or other mindfulness practices are the means by which people begin to develop this understanding. As our self-delusions dissolve, we become more sensitive to the suffering of others. As we are more sensitive to the suffering of others, our self-delusions dissolve further.
Compassion for Yourself
After all this talk of selflessness, it may seem odd to end with compassion for oneself. But it's important not to run away from our own suffering.
Pema Chodron said, "In order to have compassion for others, we have to have compassion for ourselves." She writes that in Tibetan Buddhism there is a practice called tonglen, which is a kind of meditation practice for helping us connect to our own suffering and the suffering of others.
"Tonglen reverses the usual logic of avoiding suffering and seeking pleasure and, in the process, we become liberated from a very ancient prison of selfishness. We begin to feel love both for ourselves and others and also we being to take care of ourselves and others. It awakens our compassion and it also introduces us to a far larger view of reality. It introduces us to the unlimited spaciousness that Buddhists call shunyata. By doing the practice, we begin to connect with the open dimension of our being."
Again, we see the way compassion "introduces us to a far larger view of reality." This larger view is seen by the two eyes of wisdom and compassion.